异常捕获

以前使用executor的时候，为了记录任务线程的异常退出会使用ThreadFactory来设置线程的UncaughtExceptionHandler，但是按照书上的验证发现，采用executorService.submit执行任务时，线程抛出的异常并不会被该处理器捕获，而当使用executor.execute提交任务时则会被捕获。代码如下：

        final UncaughtExceptionHandler handler = new UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(final Thread t, final Throwable e) {
                System.out.println("uncaught exception");
            }
        };

        ThreadFactory exFactory = new ThreadFactory() {
            @Override
            public Thread newThread(final Runnable r) {
                Thread x = new Thread(r);
                x.setUncaughtExceptionHandler(handler);
                return x;
            }
        };

        ExecutorService es = Executors.newSingleThreadExecutor(exFactory);
　　　　 // es.execute(new Runnable() {
        es.submit(new Runnable() {
            @Override
            public void run() {
                ArrayList<Integer> x = new ArrayList<Integer>();
                System.out.println(x.get(10)); // index out of bound
            }
        });

如果要获得submit任务的异常需要使用其返回的future对象，执行器get方法如下：

        ExecutorService es = Executors.newSingleThreadExecutor(exFactory);
        Future<Void> f = (Future<Void>) es.submit(new Runnable() {
            @Override
            public void run() {
                ArrayList<Integer> x = new ArrayList<Integer>();
                System.out.println(x.get(10));
            }
        });

        try {
            f.get();
        } catch (InterruptedException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        } catch (ExecutionException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }

此时程序会打印错误信息。